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KABUL, Afghanistan — Taliban militants killed five people in an ambush Sunday while U.S.-led coalition troops moved deeper into Afghanistan’s southern mountains in an offensive that has killed about 90 insurgents in less than a week, officials said.

More than 10,000 U.S.-led troops have spread out over four southern provinces as part of Operation Mountain Thrust, a counterinsurgency blitz aimed at quelling a Taliban resurgence.

Taliban militants ambushed a convoy carrying a former provincial chief in Helmand on Sunday, killing him and four bodyguards, said Ghulam Mohiudin, the governor’s spokesman. The former official, Jama Gul, had been traveling along a highway in the southern province.

Afghan soldiers — along with U.S., Canadian and British troops — are spreading out over Helmand, Uruzgan, Kandahar and Zabul provinces to hunt down Taliban fighters blamed for a recent surge in ambushes and bombings.

Taliban stepping up attacks
More than 500 people have been killed in the past month as insurgents, primarily Taliban, have stepped up attacks against coalition and Afghan soldiers.

British troops battled Taliban fighters on Saturday near Kajaki dam in southern Helmand province, killing six insurgents, Capt. Drew Gibson said Sunday. In the past few days, militants had been firing mortars in an attempt to damage the dam, Gibson said, adding that British forces “have tightened security in this area.”

In the past week, coalition officials said an estimated 85 other insurgents were killed in the offensive, the largest anti-Taliban military campaign undertaken since the former regime’s 2001 ouster in an American-led invasion.

The operation, which began with limited raids in May, rolled out in earnest last week to help prepare for the handover of military control to NATO forces in the southern region next month.

Military officials say the surge in fighting appears to be an attempt by the increasingly bold Taliban to seize an opportunity in the south while the government’s influence remains weak and as U.S.-led troops prepare to transfer the regional command to NATO troops from Britain, Canada, the Netherlands and Romania.

Increase in ambushes
Militants’ tactics have included increased bombings, ambushes and suicide attacks as the weather has warmed during the spring.

White House spokesman Tony Snow told CNN’s “Late Edition” the Taliban appears to be “trying to test in the south, where the U.S. forces are handing over to NATO.” He noted that U.S. airstrikes have increased along with fighting on the ground.

“The Taliban fighters have overwhelmingly been losing,” Snow said. “The government is taking control of more and more territory within Afghanistan proper — and you can expect there to be pushback by the Taliban.”

Air Force officials say the number of air bombardments in Afghanistan — about 750 in May alone — has surpassed the smaller amount of American airstrikes on Iraq.

Thousands of U.S. airstrikes
U.S. warplanes logged nearly 2,000 strikes in Afghanistan from March through May 2006, about as many as the same period in 2005, Air Force Maj. Michael Young said earlier this month. But he said airstrikes spiked at 750 last month, as opposed to 660 in May 2005.

The U.S.-led coalition invaded after the Sept. 11 attacks and toppled the hard-line Taliban government for harboring Osama bin Laden and his al-Qaida supporters.

Asked if there had been progress in the hunt for bin Laden, Snow said, “there is,” but he did not give details. Bin Laden is believed to be holed up along the border with Pakistan in rugged, remote terrain, protected by loyal tribesmen.

“I don’t want to try to characterize anything that’s going on, because the moment you try to do that, you could get in the way of ongoing activities,” Snow said. “Let’s simply say that the United States is determined to do everything in its power, and the president, in the power of the administration, to find him.”